The structure and patterns of expression of the normal counterpart of the dbl oncogene were studied. cDNAs corresponding to transcripts of the normal dbl locus were isolated and their nucleotide sequences are now being determined and compared to that of the transforming gene. Normal and tumor tissue as well as cell lines derived therefrom were screened with dbl cDNA and genomic probes. The transcript was detected in normal human brain, adrenals, testes and ovaries, and its size determined. Cloning of the whole dbl normal counterpart will allow its comparison with the biologically active gene and its mechanism of activation. It will also allow us to express the protein both in eukaryotic and prokaryotic systems in order to study its normal function.